Short term culture of human midterm and term placenta: parameters of hormonogenesis

In Vitro Culturing of Human Trophoblasts from Term Placenta

Since the early 1960s, researchers began culturing placental cells to establish an in vitro model to study the biology of human trophoblasts, including their ability to differentiate into syncytiotrophoblasts and secrete steroid and peptide hormones that help sustain a viable pregnancy. This task was addressed by testing different serum concentrations, cell culture media, digestive enzymes, growth factors, substrate coating with diverse proteins from the extracellular matrix, and so on. Among the many methodological challenges, the contamination of trophoblasts with other cell types, such as immune and stromal cells, was a matter of concern. However, introducing the Percoll gradient to isolate cytotrophoblasts was an excellent contribution, and later, the depletion of contaminating cells by using magnetic bead-conjugated antibodies also helped increase the purity of cytotrophoblasts. Herein, with some modifications, we describe a rapid and easy method for cytotrophoblast isolation from the term human placenta based on the previously reported method by Harvey Kliman et al. (Endocrinology 118:1567-1582, 1986). This method yields about 40-90 million cells from a single placenta, with a purity of around 85-90%.

Placental Trophoblast Cell Isolation from the Term Placenta

Multiple cell lines have been utilized over time in studying placental biology. Still, most of them rely on choriocarcinoma cells or immortalized trophoblast cells that may not be entirely comparable with actual human placental trophoblast cells. Term placentas can be a source of primary villous trophoblasts. However, challenges remain in isolating them and maintaining them in extended culture. This manuscript describes our three-phase protocol utilizing enzymatic/mechanical digestion, modified Percoll gradient density separation, and immunopurification using magnetic beads. The resulting trophoblast culture remains viable for an extended period and highly pure after initial passaging.

Regulation of hormone production in the human feto-placental unit

Hormone production in the human feto-placental unit has been studied extensively yet relatively little is known about the regulatory mechanisms involved. A tissue culture approach has been used to examine the effect of potential controlling factors on steroid production by the human mid-term fetal adrenal and mid-term and term placenta. Adrenal. The pituitary peptides corticotropin (ACTH) and alpha-melanocyte-stimulating hormone (alpha-MSH) had the most significant influence on adrenal steroidogenesis in both the fetal and definitive zones. Their effects were not identical: they enhanced dehydroepiandrosterone sulphate (DHA-S) production in a comparable manner but alpha-MSH had much less of a stimulatory effect on cortisol biosynthesis. Medium from homologous fetal pituitary cultures mimicked the effects of alpha-MSH rather than ACTH. Homologous placental culture medium and progesterone enhanced only cortisol production and only in the fetal zone cells. These results demonstrate that specific fetal pituitary and placental factors influence fetal adrenal activity and suggest a functional zonation of the fetal adrenal. Placenta. DHA, DHA-S and 16-hydroxy-DHA stimulated oestrogen biosynthesis while high concentrations of DHA and DHA-S (but not 16-hydroxy-DHA) inhibited progesterone production. Luteinizing hormone-releasing hormone (LRH) inhibited both oestrogen and progesterone biosynthesis. Placental steroidogenesis can therefore be influenced not only by the fetus, through its increasing adrenal output of oestrogen precursors, but also by factors originating within the placenta itself.

Effect of leptin on the regulation of placental hormone secretion in cultured human placental cells

Placenta is an important source of leptin during pregnancy that contributes to the high plasma leptin levels in pregnant women. Leptin and its functional receptors are synthesized in trophoblast cells that, in turn, secrete gestational hormones supporting a paracrine or autocrine role for leptin in the endocrine activity of the placenta. In the present study we examined the effect of leptin on in vitro release of gestational hormones (human chorionic gonadotropin (hCG), human placental lactogen (hPL), progesterone, estrogens and testosterone) by human term placental cells in culture. Placentas at term were obtained immediately after delivery from mothers with uncomplicated pregnancies. Progesterone, hCG, hPL, estradiol, estrone, estriol and testosterone levels were measured by different assays in culture media of cells maintained in monolayer culture after incubation for 12, 24, 48 or 72 h with leptin or placebo. Incubation with leptin did not modify hCG, hPL, progesterone, estriol and estrone secretion for any of the doses and times assayed. However, leptin led to a dose-dependent decrease in estradiol release. This effect was observed when treatment with recombinant human leptin spanned from 12 to 72 h. At this time an increase in testosterone levels was observed in leptin-treated cells versus placebo. These results indicate that leptin can be considered a gestational hormone implied in the endocrine function of the placenta, with an important role in control of the production of steroid reproductive hormones in placental cells in vitro.

Progesterone and human placental lactogen inhibit leptin secretion on cultured trophoblast cells from human placentas at term

The placenta is an important source of leptin production that contributes to the state of hyperleptinemia observed in pregnant women. Moreover, the synthesis of leptin and its receptors by syncytiotrophoblast cells suggests a potential paracrine or autocrine action of leptin in the placenta. In the present study we examined the effect of gestational hormones, human chorionic gonadotropin (hCG), human placental lactogen (hPL), progesterone and estradiol, on in vitro leptin release by human term trophoblast cells in culture. Placentas at term were obtained immediately after delivery from mothers with uncomplicated pregnancies. Leptin levels were measured by enzyme-linked immunosorbent assay in culture media of trophoblasts maintained in monolayer culture for 24, 48 and 72 h with different hormonal treatments or placebo. Treatment with hPL and progesterone led to a time- and dose-dependent decrease in leptin release that was statistically significant after 24 h, with a maximal effect after 72 h of incubation. In contrast, incubation with estradiol and hCG did not have exhibit any effect on leptin secretion at any of the doses and times assayed in this work. The results obtained in this study support that leptin can be considered a gestational hormone implied in the endocrine function of the placenta and that its secretion is at least partially regulated by steroid and peptidic reproductive hormones in trophoblast cells in vitro.

Human villous macrophage-conditioned media enhance human trophoblast growth and differentiation in vitro

In human chorionic villi, numerous macrophages, so-called Hofbauer cells, are located adjacent to trophoblasts. To determine the role of the macrophages in the proliferation and differentiation of trophoblasts, cytotrophoblast cells were cultured in serum-free culture-conditioned media of villous macrophages (VMCM), peritoneal macrophages (PMCM), and villous fibroblasts (VFCM). In VMCM, proliferation of cytotrophoblast cells was detected at 24 h by immunocytochemistry with Ki-67-antibody. A large number (P < 0.001) of multinucleated syncytia was formed in VMCM. In VMCM, cytotrophoblast cell fusion was completed by 96 h, which coincided with the peak of hCG secretion and initiation of human placental lactogen (hPL) release. Levels of hCG (P < 0.001) and hPL (P < 0. 001) secretion from syncytial cells were significantly higher in VMCM than in PMCM or in VFCM. Concentrations of macrophage colony-stimulating factor (M-CSF) and vascular endothelial growth factor (VEGF) analyzed by ELISA were greater in VMCM than in PMCM or in VFCM, whereas monocyte chemoattractant protein-1 (MCP-1) concentration was high in PMCM. The expression patterns of M-CSF, VEGF, and MCP-1 in villous macrophages and peritoneal macrophages by reverse transcriptase-polymerase chain reaction were similar to their secretion patterns. Thus, villous macrophages have a greater ability to stimulate hCG and hPL secretion than do peritoneal macrophages. This study suggests that macrophages within the villous stroma may stimulate the growth and differentiation of trophoblasts through their secreted substances.

Techniques to study human placental transport

Pregnancy in the 20th century involves women of many age groups from early teens to the fourth or fifth decade. Modern medicine and in vitro fertilization techniques have increased options for pregnancy and childbirth. Pregnancy is a dynamic state, and medical concerns may involve disorders of the fetus and mother requiring medications and special nutrients. Therefore, different techniques have been developed to evaluate the placental transfer of drugs and nutrients using tissues and cells derived from human placenta. These include (a) isolated tissues and cells to study placental transport, (b) primary and malignant trophoblast cell cultures and (c) biophysical methods for studying placental transport. Also, convenient study models have been developed to evaluate placental transfer of safe drugs in pregnant women. Some of the drugs studied by these techniques and models include (a) anesthetics and pain medications used during delivery, (b) antibiotics and anti-bacterials used to cure infections, (c) drugs abused by pregnant women and (d) nutrients required for proper fetal growth. Placental transfer and exchange mechanisms are complicated processes, and in vitro models reflect only partially the equilibria that exist among mother, placenta and fetus. The perfused cotyledon model is elegant and simple but gives only restricted information. Isolated placental tissues give useful information about the pharmacological effects of drugs. Metabolic studies using human placental models provide information on the metabolism of a drug during placental transfer and accumulation of the drug or its metabolite in the placenta or fetal circulation. Several studies on the transplacental passage of drugs exist but many questions regarding the transfer of drugs between the maternal and fetal circulations and clearance of drugs from fetal circulation have yet to be answered. This article reviews in vitro and in vivo methods for evaluation of transplacental transport of drugs and their current effectiveness to obtain clinically useful data.

Culture of syncytiotrophoblast for the study of human placental transfer. Part II: Production, culture and use of syncytiotrophoblast

The conditions necessary for producing syncytical syncytiotrophoblast are examined. Tissue disaggregation conditions, culture media composition, different extracellular matrices and the influence of placental gestational age are all assessed. The importance of evaluating the biochemical and functional differentiational state of the cells is also stressed. Evidence is summarized that syncytiotrophoblast in culture is morphologically and ultrastructurally very similar to syncytiotrophoblast in vivo, and what is so far known biochemically is largely consistent with what is known in vivo. Studies published to date on microvillous membrane uptake and release and relationships with intracellular metabolism using syncytiotrophoblast in conventional culture are outlined from the point of view of the advantages and potential of this model. The present state of development of the two-sided model is assessed, mentioning factors to be considered such as the supporting membrane to be used, accounting for passive diffusion and paracellular leak components of transport and dealing with quantitative effects in kinetic studies of the presence of the supporting membrane. It is concluded that satisfactory methods are now in place for preparing pure villous syncytial syncytiotrophoblast in culture from cytotrophoblast derived from term (but not early) placentae, suitable for studying microvillous membrane transport and relationships with intracellular metabolism. Cytotrophoblast from early gestational age placenta may require different conditions to form true syncytiotrophoblast. A two-sided model for studies of overall transfer, basal transport and basal control mechanisms is now available and possibly with some development should be a good model for such investigations.

Culture of syncytiotrophoblast for the study of human placental transfer. Part I: Isolation and purification of cytotrophoblast

Criteria for a successful model for the study of trans-syncytiotrophoblast transfer include isolating substantially pure trophoblast cells from placental villous tissue, and obtaining from them phenotypical villous syncytial syncytiotrophoblast during culture. For studies involving the basal membrane, including overall transfer, basal uptake and output, and controls acting at the basal membrane, a two-sided model is required with a separate compartment of culture medium in contact with the basal cell surface. All current methods of isolating cytotrophoblast, the precursor of syncytiotrophoblast, derive from the original tissue trypsinization method of Thiede (1960), which produces cultures of villous cytotrophoblast cells contaminated with other placental cell types. Lessons learned from successful and unsuccessful development of the model over 35 years are outlined, and recently established methods for purifying the isolated mixed cells discussed. These include sedimentation and centrifugation methods, immunological and receptor binding methods, and more selective release of trophoblast cells from tissue. Immuno flow cytometric cell sorting methods are potentially capable of isolating subpopulations of various phenotypical trophoblast types. We conclude that satisfactory methods are now available for isolating and purifying cytotrophoblast from early or late gestation human placenta.

Superfused microcarrier cultures of choriocarcinoma cells: a dynamic model for studying transport of glucose and amino acids

We here describe a novel procedure for culturing BeWo and JAr choriocarcinoma cells on solid microcarrier beads. The regime developed to stir the beads resulted, after about 10 days, in small aggregates of two to six beads covered with a layer of differentiated cells. Bead aggregates were packed into small columns and superfused, providing a dynamic in vitro system for studying the uptake mechanisms for sugars and amino acids. The rapid, unidirectional uptake of tritiated L-phenylalanine, L-serine, L-arginine and D-glucose was determined, relative to an extracellular reference tracer, in cells superfused in 0.5 ml (range 0.3-0.8 ml) columns. Several sequential measurements could be made in the same column. Twenty-four hour pre-incubation with dexamethasone (0.25 microM) was found to increase the transport of D-glucose. Uptake of D-glucose was reduced by over 80 per cent following 20 min perfusion of the cells with 1 mM phloretin. Pre-incubation with growth hormone (0.2 microgram/ml) decreased the transport of serine, whereas nicotine (0.5 microgram/ml) decreased both serine and phenylalanine uptake. Atropine (1 mM) or 5-oxoproline (0.5 mM) had no short-term effects on amino acid uptake. Insulin (12.5 mIU/ml) had no effect on the transport of the amino acids but caused a small but significant increase in glucose transport (P < 0.05). This model allows characterization of human trophoblast function without the complications resulting from the presence of other cell types in placental slices or fragments.

Ferritin in cultured human cytotrophoblasts: synthesis and subunit distribution

The present study aims at the role of ferritin in the regulation of syncytiotrophoblast free iron levels. The differentiated cytotrophoblast cell in culture is used as a model for this maternal-fetal interface. Cytotrophoblast cells isolated from term placentae are cultured in iron-poor (Medium 199), iron-depleted [desferrioxamine(DFO)] and iron-supplemented [diferric transferrin (hTF-2Fe), ferric ammonium citrate (FAC)] medium. Distribution and de novo synthesis of isoferritins is studied, together with the cellular iron concentration and the ferritin iron saturation. Compared to ferritin isolated from total placenta, ferritin obtained from villous tissue is enriched with acidic isoforms. This observation is in agreement with measured light (L) to heavy (H) subunit ratios < 1 of de novo synthesized ferritin in cultured cytotrophoblast cells. Neither iron-poor culture medium, nor hTf-2Fe supplemented medium affects the cellular iron or ferritin concentration. FAC increased the cellular ferritin iron saturation and (by synthesis) the acidic isoferritin concentrations. The results strongly suggest, that the term syncytiotrophoblast is able to balance transferrin-mediated iron uptake and iron release. In case of FAC supplementation, the syncytiotrophoblast is unable to keep intracellular iron low, and ferritin synthesis is stimulated. The predominance of acidic ferritins and the preferential synthesis of H subunits can be functionally explained by the established fact that iron incorporation in acidic ferritins is faster due to the presence of ferroxidase centres. Damage by free iron catalysed hydroxyl radical formation is therefore minimized.

The effect of different iron compounds on transferrin receptor expression in term human cytotrophoblast cells

During pregnancy, the mother is faced with an increased food demand. A good example of this increased demand is iron (Fe). Fe is needed in all growing cells. During pregnancy, the Fe transport to the fetus increases enormously. This amount can easily induce an Fe deficiency in the mother. Fe supplementation is very important for her, but not for the Fe status of the fetus, which is protected against Fe toxicity as well as deficiency. The placenta seems to be autonomous in Fe uptake. Likely there is a regulation mechanism. The human placenta is hemomonochorial. The cell layer of the fetus in contact with the maternal blood is formed by syncytiotrophoblasts. Fe is transported to the placenta by transferrin. Transferrin binds to a transferrin receptor on the trophoblast membrane and is internalized via an endocytic pathway. During this cycle, Fe is released from transferrin and the transferrin-transferrin receptor complex is recycled to the membrane. Isolated trophoblast cells from term placentas form a syncytium in vitro, and transferrin receptors are expressed. Expression depends on the number of cells in culture, culture time, the amount of Fe available, and the Fe compound. By regulation of the number of transferrin receptors, trophoblasts are able to control their Fe uptake.

Ethanol decreases progesterone synthesis in human placental cells: mechanism of ethanol effect

Fetal alcohol syndrome (FAS) is a set of signs and symptoms in offsprings born to mothers who abuse alcohol during pregnancy. We postulated that impairment in the placental endocrine function contribute to FAS. In this study, we examined in vitro effects of ethanol on the placental cells' (cytotrophoblast cells) capacity to synthesize progesterone. Cytotrophoblast cells were isolated from normal term placenta and were incubated (2 x 10(6)) with 20-, 30-, and 40-mM doses of ethanol for 6 h. Progesterone was measured in the incubate by RIA. The results showed that, at the 20-mM dose of ethanol, progesterone synthesis was significantly decreased (p less than 0.01), at the 30-mM dose level there was a further decrease of 20%. The differences between 30- and 40-mM ethanol dose levels were not significant. To determine the mechanism of ethanol effects on progesterone synthesis, cytotrophoblast cells were preincubated with 30 mM ethanol followed by 10 microliters of LDL (10 microliters LDL = 80 micrograms cholesterol) and vice versa. The results showed that ethanol effects on progesterone synthesis was dependent on whether ethanol was added prior to or following the addition of LDL in the medium. If ethanol was added in the medium prior to LDL, progesterone synthesis was decreased significantly (p greater than 0.01); however, when ethanol was added after the LDL, ethanol had no effect on progesterone synthesis. In the experiment where ethanol and LDL were added simultaneously in the medium, ethanol blunted the stimulatory effect of LDL on progesterone synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Markers for human placental trophoblasts in two-dimensional gel electrophoresis

Primary cultures of trophoblasts established from human term placentae showed high viability and reproducibility. Two-dimensional gel patterns obtained by metabolically labeling the trophoblasts with [35S]-methionine demonstrated that their pattern of gene expression was stable during the 6-d period investigated. Gel analysis demonstrated the keratins 7, 8, 14, 17, 18, and 19. Analysis of the gel pattern confirmed the presence of a small proportion of contaminating fibroblasts and lymphocytes. The gel patterns were compared with that of skin fibroblasts, peripheral lymphocytes, and epithelial cells to identify a group of proteins that are enriched in the trophoblasts and thus may be used as marker for these cells.

A serum-free system for culturing human placental trophoblasts

We have compared hormone production by early gestation and term human placental trophoblasts cultured in Ham's F10 medium containing 10% fetal bovine serum with that by cells cultured in serum-free HB102 medium. Mean daily production of progesterone on Days 3 to 7 was approximately 25% less by both early gestation and term cells cultured in HB102 as compared to Ham's F10, but production was maintained at a stable level for at least 7 d longer than the cells in Ham's. Estradiol production from 10(-6) M dehydroepiandrosterone by both early gestation and term cells was comparable in both media. Human placental lactogen production on Days 3 to 7 was 40% less by cells cultured in HB102. Human chorionic gonadotropin (hCG) output by early gestation cells was also 50% less in HB102 but term cells in HB102 produced twice as much hCG as those in Ham's F10. 3B-Hydroxysteroid dehydrogenase (3BHSD) activity in early gestation and term cells and 11B-hydroxysteroid dehydrogenase (11BHSD) activity of early gestation cultures was comparable in the two media. 11BHSD activity was decreased in the term cultures, and this decrease was more marked in Ham's than in HB102. Sulfatase and aromatase activities in the early gestation cultures were comparable in both media; sulfatase activity was comparable and aromatase activity only 20% less in the term cells cultured in HB102. These results indicate that serum-free HB102 supports differentiated function of human trophoblast cells and is useful for studies of placental activity for as long as 14 d in culture.

Placental steroid hormones

The intent of this review was a selective consideration of recent advances in understanding placental steroidogenesis in humans. While we have omitted material, both intentionally and unintentionally, we hope this discourse presents a flavour of the current molecular endocrinology of placental steroidogenesis. In particular, advances in knowledge as it relates to the enzymes involved in progesterone and oestrogen metabolism have been addressed and correlated with placental development. Finally, because relatively less is known about regulation of steroidogenesis in the human placenta beyond the aspects of growth and differentiation, we have discussed regulation in general terms using recent data obtained in animal species.

Oestrogen synthetase (aromatase) and hormone secretion in primary cultures of human placental trophoblast cells. Effects of cyclic AMP addition at the start of culture in attached and unattached cell populations

Term placental trophoblast cells, released by trypsin digestion of placental villi, purified on a Percoll gradient and grown in serum-containing medium, differentiate within 24 to 48 h in culture from mononucleated cytotrophoblast-like cells at the start of culture to highly multinucleated giant (syncytiotrophoblast-like) cells that are more active in hormonogenesis. To determine the changes in hormone biosynthesis and secretion that occur early in the trophoblast differentiation process in vitro, freshly isolated placental cells were cultured in Dulbecco's Modified Eagle's Medium (DMEM) containing 20 per cent FBS, in the presence and absence of cAMP for up to 48 h. Cell attachment and growth, oestrogen synthetase (aromatase) activity in attached and unattached cells, and secretion of human chorionic gonadotropin (hCG) and progesterone were studied. The aromatase specific activity, low in freshly isolated cells, increased fourfold in attached cells by 3 h, and achieved a 10- to 15-fold increase by 40 to 48 h. In attached cells grown with cAMP, aromatase activity was further stimulated by about fourfold, relative to the control. The aromatase activity of the unattached cells removed from the culture dishes at various times up to 48 h showed a biphasic response: the activity decreased by 18 h and then increased back to the fresh cell levels. The effect of cAMP on aromatase in these unattached cells was manifested by a two-fold stimulation of activity by 18 h, relative to control unattached cells. Secretion of hCG from both attached and unattached cells remained at a low level (less than 200 ng/mg protein) in control cells; in the presence of cAMP, hCG secretion was stimulated by tenfold after 40 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of pure villous cytotrophoblast from term human placenta using immunomagnetic microspheres

A procedure has been developed which yields a pure population of villous cytotrophoblast from term human placenta. As a first step, a cell preparation highly enriched for cytotrophoblast (identified by positive cytokeratin staining) was obtained using a modification of the method of Kliman et al. (1986). The remaining contaminating cells (identified by positive vimentin staining) were then removed by treatment with mouse monoclonal antibodies against class I and class II major histocompatibility antigens followed by magnetic microspheres coated with goat anti-mouse IgG. The rationale for this step was based on the fact that villous trophoblast fails to express HLA antigens whereas cells from the villous mesenchyme do express these surface antigens. Rosetted cells were immobilized using a magnet allowing the non-rosetted cells to be easily withdrawn by pipette. When the non-rosetted cells were placed in primary culture, no HLA-positive or vimentin-positive cells could be detected using immunofluorescence microscopy, indicating complete removal of these components by the immunomagnetic separation procedure. The cells were positive for cytokeratin and, after 24 h, showed positive staining for pregnancy-specific beta 1-glycoprotein (SP1) and human chorionic gonadotropin. Recovery of cytotrophoblast was greater than 92% with only a slight loss of viability.

Ultrastructural changes and immunocytochemical analysis of human placental trophoblast during short-term culture

Trophoblastic cells, of at least 95 per cent purity by immunofluorescence and morphological criteria, were obtained from human term placenta by a simple trypsinisation method without the additional purification steps or complex culture conditions used by others. The differentiation of these cells was followed over four days in culture by fluorescence immunocytochemistry, by scanning and transmission electron microscopy and by light microscopy. The results support the idea that the isolated cells are cytotrophoblast and that these differentiate during this time into cells with characteristics of villous syncytiotrophoblast. This process involved first the formation of a multicellular layer of mononucleated cells, then the development of a syncytium of multinucleated cells and, not necessarily concurrently, functional differentiation. This may be a useful model for the study of syncytiotrophoblast function.

The appearance of transferrin receptors on cultured human cytotrophoblast and in vitro-formed syncytiotrophoblast

Using trypsinization and Percoll gradient centrifugation, mononuclear cell populations were prepared from human term placentae. These populations consist mainly of cytotrophoblast, which probably lacks transferrin receptors. In vitro, transferrin receptors appear on these mononuclear cells and on syncytiotrophoblast formed in vitro, independently, of cellular fusion and proliferative state.

Effects of cyclic adenosine monophosphate on human chorionic gonadotropin and estradiol output by cultured human placental cells

We have previously shown that adenosine-3',5'-cyclic monophosphate (cAMP) inhibits basal estradiol output in human trophoblast cells. The objective of this study was to investigate further the effect of 8-bromo-cAMP on the conversion of C19 androgens to estradiol by placental cells. Trophoblast cells were prepared from human term placenta and maintained in monolayer culture. On days 3 and 4 of culture, these cells were treated with dehydroepiandrosterone sulfate, androstenedione, or testosterone with or without the concomitant presence of 8-Br-cAMP. 8-Br-cAMP markedly enhanced human chorionic gonadotropin secretion into the culture medium. On the other hand, the concomitant addition of 8-Br-cAMP with the androgen precursors led to an inhibition of estradiol output. The concentrations of androstenedione and dehydroepiandrosterone in the culture medium after treatment with dehydroepiandrosterone sulfate were elevated by the concomitant presence of 8-Br-cAMP. From these results we conclude that 8-Br-cAMP enhances human chorionic gonadotropin output in human term placental cells, whereas the presence of 8-Br-cAMP in cells given androgen precursors inhibits estradiol output, probably at the level of aromatization.

Differential effects of 8-bromo-cyclic AMP on human chorionic gonadotropin (hCG), progesterone and estrogen production by term placental cells

The present study examined the effects of a cAMP analog on the output of hCG and progesterone (P) in human term trophoblast cells in culture, as well as the conversion of androstenedione and testosterone to estradiol--17 beta and estrone by these cells. The levels of hCG and P in the culture medium increased throughout the four-day culture period. Addition of 8-bromo-adenosine-3',5'-monophosphate (8-Br-cAMP), forskolin or cholera toxin (but not 8-Br-cGMP) stimulated hCG and P production by the cultivated placental cells. In contrast, the presence of 8-Br-cAMP for 2 days significantly decreased basal estradiol-17 beta output, as well as conversion of androstenedione to estradiol-17 beta; the conversion of androstenedione to estrone was not affected. 8-Br-cAMP attenuated the conversion of testosterone to both estradiol-17 beta and estrone. These results further support the view that cAMP could have both stimulatory and inhibitory actions on placental hormonogenesis.

Isolation and characterization of rat trophoblast cells

Previous immunohistochemical studies of the rat placenta using specific alloantisera and/or monoclonal antibodies showed that the basal zone trophoblasts stained for Pa and Aa class I major histocompatibility complex (MHC) antigens and for the human SP1-related antigen. In an effort to isolate the basal zone trophoblast cells from the rat placenta, we used these markers to assess the degree of purification of the cells separated by density gradient centrifugation using either Ficoll-Hypaque or Percoll as the gradient medium. The cells were put either on the top or at the bottom of discontinuous density gradients in the range of 1.005-1.10 g/ml. The cell separation profiles for the two media were different. With Percoll, most of the trophoblast cells (80-95%) were collected at the density gradients 1.04/1.06 and 1.06/1.08, whereas with Ficoll-Hypaque, these gradients separated only a small fraction (4-23%) of the trophoblast cells, and most of them pelleted at the bottom of the tube. The trophoblast cells separated by Ficoll-Hypaque, however, showed fewer contaminant cells than those separated by the Percoll gradients.

Antifertility actions of the progesterone antagonist RU 486 include direct inhibition of placental hormone secretion

the antifertility effects of the potent antiprogestin RU 486 (mifepristone) during early pregnancy have been attributed to its blockade of progesterone receptors in the endometrium. Studies in cultured syncytiotrophoblasts have revealed an additional action of RU 486 at the placental level, where it impairs the production of human chorionic gonadotropin (hCG), human placental lactogen (hPL), and progesterone. RU 486 (10 nmol-10 mumol/l) attenuated the production of all three placental hormones, in a dose-related manner, and its effects on hCG and hPL were reversed by addition of exogenous progesterone. The specific inhibitory effects of RU 486 on placental hormone secretion indicate that its antifertility actions are attributable to competitive inhibition of progesterone action in the trophoblast as well as in the endometrium.

Estrogen synthetase (aromatase) in cultured human term placental cells and neoplastic human trophoblast

Estrogen synthetase (aromatase) is present in large amounts in human term placenta. However, the localization of aromatase within the cellular structure of the placental villus is obscure. By immunocytochemical techniques using antibodies that separately recognize each component of the aromatase cytochrome P-450 enzyme system, the fraction of term placental trophoblast cells in primary culture expressing each aromatase component antigen increased from 20% in fresh mononucleated cells to about 65% for multinucleated giant cells after 72 h. In contrast, about 80% of human choriocarcinoma cells in continuous culture (JAr line) expressed each aromatase component antigen. The fraction of trophoblast cells in primary culture containing human chorionic gonadotropin increased from about 14% in fresh mononucleated cells to about 45% after 72 h and was about 30% in the choriocarcinoma cells. Fibroblast cells in culture, derived from trypsin-treated placental villi, contained aromatase activity, albeit much lower than term placental trophoblast cells. Aromatase specific activity in these placental fibroblasts did not change following growth with dibutyryl cAMP plus theophylline for 72 h.

Effects of adenosine 3',5'-cyclic monophosphate, forskolin, and cholera toxin on hormone production in human term placental cells

Trophoblast cells from human term placenta in monolayer culture were used to investigate the role of adenosine 3',5'-cyclic monophosphate in the production of human chorionic gonadotropin and estradiol-17 beta. The intracellular concentration of adenosine 3',5'-cyclic monophosphate was elevated by (1) addition of an adenosine 3',5'-cyclic monophosphate analogue, 8-bromoadenosine 3',5'-cyclic monophosphate, (2) inhibition of the hydrolysis of Gs-GTP complex by cholera toxin, and (3) direct stimulation of adenylate cyclase with forskolin. Addition of 2 mmol/L of 8-bromoadenosine 3',5'-cyclic monophosphate markedly increased the accumulation of human chorionic gonadotropin in the culture medium on days 2, 3, and 4 of treatment. Likewise, addition of cholera toxin (0.2 microgram/ml) or forskolin (50 mumol/L) also enhanced human chorionic gonadotropin production. On the other hand, the production of estradiol-17 beta was significantly inhibited by 8-bromoadenosine 3',5'-cyclic monophosphate, at the same time that human chorionic gonadotropin production was enhanced in the same experiments. These results further support a differential role of adenosine 3',5'-cyclic monophosphate on human chorionic gonadotropin and estradiol-17 beta production in the human term placenta.

Ultrastructural visualization of the internalization of low density lipoprotein by human placental cells

Low density lipoproteins (LDL) were conjugated to colloidal gold to visualize the route for internalization of LDL in the cultured cells of human term placenta. Cells were obtained from placental villi (caesarian section) by a standard trypsin-DNase dispersion method followed in some cases by a Percoll gradient centrifugation step. Employing electron microscopy it was observed that after 3 days of culture, cells obtained by trypsin-DNase dispersion were a mixture of macrophages, mononucleated cells and large multinucleated cells. When the cells were incubated for 3 days after the Percoll purification, essentially multinucleated cells identical to the syncytiotrophoblast were present. The number of LDL receptor was increased by preincubation in medium with lipoprotein depleted serum. In binding experiments cells incubated at 4 degrees C for 2 h with medium containing gold LDL conjugates showed gold LDL attached to the plasma membrane without characteristic localization. After incubation with gold LDL at 37 degrees C for various times, the three cellular types showed ligand internalization. Gold LDL endocytosis involved first coated pits but also uncoated plasmalemmal invaginations. Then gold LDL was further observed in coated and non coated vesicles, smooth walled endosomes, multivesicular bodies and tubular vesicles. Lastly free gold particles were observed in lysosome like dense bodies. These results prove the internalization of gold LDL conjugates by human cultured placental cells, particularly by syncytiotrophoblast like multinucleated cells. This accumulation of LDL (the major cholesterol carrying protein in humans) is recognised to be responsible for the exogenous cholesterol supply indispensable to the progesterone biosynthesis and cellular growth of the placenta.

Critical factors in establishing monolayer cultures of normal human placental cells in serum-free medium

Comparative studies have been performed to determine the best method for preparing monolayer cultures of normal human term trophoblast cells. The use of 0.25% trypsin-10 U/ml DNAse I provided the highest cell viability and greatest hormone production, but was critically dependent on the trypsin lot used. Cell function in culture was not improved with various substrata, nor did other factors (medium type, pH, red blood cell removal) affect the results. Optimization of dispersal and culture conditions permitted the trophoblast cells to survive with intact hormone secretion and response to secretagogues under serum-free conditions. These studies thus define the best methodology for establishing trophoblast cells in monolayer cultures.

The effect of inhibitors on insulin regulation of hormone secretion by cultured human trophoblast

The effect of insulin in physiological concentrations on hormone secretion by human term trophoblast cell culture was studied in relation to insulin control of glucose transport and utilization. Specific inhibitors to these 2 functions were added to the culture, either alone to test for a dose response or with insulin. 2-Deoxy-D-glucose, which inhibits glycolysis, did not change the pattern of response of estradiol and placental lactogen (hPL) secretion to insulin. Phloridzin, an inhibitor of glucose transport, interfered with the stimulatory effect of insulin on hPL secretion, but stimulated insulin inhibition of estradiol secretion when added by itself. The results indicate that hPL response to insulin is dependent on glucose transport, but is independent of glycolysis. Estradiol response is dependent on glucose transport, but is independent of glycolysis.

Preservation of human chorionic gonadotropin and placental lactogen secretion and normal morphology following long-term culture of normal human placental cells

In order to study the regulation of hCG and hPL secretion during gestation, a system for the preservation of the functional integrity of normal placental cells in long-term culture was established. Normal term placental cells were dispersed with 0.25% trypsin-500 units DNAse I and cultured in a monolayer in Dulbecco's modified Eagle medium with 10% fetal bovine serum. Normal cell morphology, basal hCG and hPL production and hCG responses to dibutyryl cAMP were preserved till 54 days of culture. This model may be useful for the study of long-term regulation of normal placental hCG and hPL synthesis and secretion.

Long-term culture of human trophoblast cells

A technique is presented for the preparation of cultures of replicating human trophoblast cells from term placentas. The adherent cells obtained were very slow growing (doubling time 12.5 days) as measured by the rate of increase in cell protein, [14C]-leucine uptake and cell number. Cells from individual placentas have been maintained in continuous culture for up to 1 year (10-12 passages) and have been successfully recultured after storage in liquid nitrogen. Cultured cells showed positive immunofluorescent staining for human placental lactogen, human chorionic gonadotrophin, transferrin and type IV collagen. The adenine nucleotide content indicated that energetically the cells were in balance even after prolonged culture.

The modulation of placental lactogen secretion by calcium: studies with cultured human term trophoblast

Previous reports have documented the negative regulatory effect of calcium ion on the secretion of human placental lactogen by the placenta. Human term trophoblasts were dispersed from term placenta and maintained in monolayer cell culture. Incubation of the cultured trophoblast with EGTA produced a dose-dependent stimulation of placental lactogen secretion. The calcium ionophore A23187 inhibited hormone secretion. This inhibitory effect was eliminated by the addition of the calcium-calmodulin complex inhibitor trifluoperazine. It is concluded that calcium exerts a negative regulatory effect on the secretion of placental lactogen by a mechanism which requires the action of the calcium-calmodulin complex.

Purine re-utilization in normal and malignant cells of human placental origin

The metabolism of the purine compounds adenine, hypoxanthine and adenosine, was studied in cultured human choriocarcinoma cells (BeWo) and in term human placental cells in primary culture. Both preparations retained at least some specific placental functions, as shown by secretion of human chorionic gonadotrophin, which was less in the malignant cell line than in the primary culture. In contrast, choriocarcinoma cells incorporated substantially more purine bases (adenine and hypoxanthine) and nucleoside (adenosine) into nucleotides, mainly ATP. Adenosine metabolism was concentration-dependent, with a higher proportion metabolized to hypoxanthine at higher substrate concentration. The term placental cells, which do not divide in culture, have a less active purine metabolism, but they retain a degree of specialized function higher than that of malignant cells of placental origin.

Effect of adrenergic agonists on progesterone production by human placental cells in culture

Human placental cells maintained were used to determine the direct effect of beta-adrenergic agonists on progesterone accumulation by the placenta. In five studies, when either of the beta-adrenergic receptor agonists, terbutaline or isoproterenol, 1.5 micrograms/ml, was incubated for 24 hours with the placental cells, significantly more progesterone was present in the culture medium than in the medium of matched controls. Compared with the medium of matched controls, progesterone in medium increased 36 +/- 6% (mean +/- SE) when cells were treated with terbutaline and 38 +/- 7% when cells were treated with isoproterenol. In two dose-response studies with terbutaline, a minimal dose of 0.15 micrograms/ml was required to significantly increase progesterone in medium compared with that in matched controls. In three studies, propranolol at a concentration of 1.5 micrograms/ml completely blocked the stimulatory effect of 1.5 micrograms/ml of terbutaline.

Suppression of human chorionic gonadotropin by progestational steroids

The dynamics of the secretion of human chorionic gonadotropin (hCG) were studied by culturing explants of normal term placentas for as long as 144 hours. A significant accumulation of immunoreactive hCG (beta-subunit) was first detected at 48 to 72 hours, and a sixfold increase in hCG was observed in control culture medium at 144 hours. Compared to control cultures, progesterone (P < 0.001) in physiologic tissue levels of 5 to 20 micrograms/ml, pregnenolone (P < 0.001), 20 micrograms/ml, and 20 alpha-dihydroprogesterone (P < 0.001), 20 micrograms/ml, suppressed the secretion of hCG throughout the study period. Progesterone decreased the secretion of hCG in a dose-response manner (r = -0.8S87, P < 0.1). No suppression of hCG was observed in the presence of cortisol, testosterone, dihydrotestosterone, 17 beta-estradiol, or estriol. The secretion of human chorionic somatomammotropin was unchanged in the presence of progesterone. The augmented hCG response in the presence of dibutyl cAMP (P < 0.001) was significantly, but not completely, suppressed by progesterone 20 micrograms/ml culture medium (P < 0.01). Under these conditions progestational steroids or their immediate metabolites suppress the secretion of hCG, and they may be responsible for the decline in the levels of hCG during pregnancy.

Preparation of highly purified cytotrophoblast from human placenta with subsequent modulation to form syncytiotrophoblast in monolayer cultures

The preparation of highly purified monolayer cultures of human cytotrophoblast cells essentially free of stromal and syncytial cells is described. Such cells subsequently form multinucleate syncytial cells in vitro. This is accompanied by the synthesis of heat-stable alkaline phosphatase and beta-HCG. A significant proportion of the multinucleate cells that form in monolayer cultures of early placentae arise as a result of an amitosis. It is suggested that this in vitro behavior may reflect an in vivo process.

Effects of culture conditions on the synthesis of human chorionic gonadotropin by placental organ cultures

Culture conditions for maintaining first trimester human placenta in organ culture, which enhance the secretion of human chorionic gonadotropin (hCG), are described. Nutrient medium, oxygen tension and Gelfoam support matrix influence the synthesis of hCG by these cultures. Placental tissue remained viable for the duration of experiments (12 days) as judged by the incorporation of tritiated thymidine into DNA and the lack of release of incorporated [125I]iododeoxyuridine. Optimal conditions for hCG synthesis in placental organ culture included an atmosphere of 95% air and 5% Co2 (approximately 20% O2), CMRL 1066 medium containing fetal human or bovine serum, insulin, hydrocortisone and retinal acetate. Multiple pieces of placenta could be cultured in the same dish with an additive effect on hCG secretion. The functional responsiveness of these placental cultures was demonstrated by modulation of hCG synthesis with theophylline and 3'5' dibutyryl cyclic AMP.